Smoking articles, such as cigarettes, cigars, and the like, are conventionally made by wrapping a column of tobacco in a wrapping paper. At one end, the smoking article may, for example, include a filter through which the article is smoked. Filters can be attached to a smoking article using a tipping paper that is glued to the white wrapping paper. The wrapping papers and tipping papers used to construct smoking articles are typically made from flax or other cellulosic fibers and contain a filler, such as a calcium or magnesium compound.
Besides being used to hold the cigarette together and to provide the cigarette with an aesthetic appearance, wrapping papers also contribute to or control many physical properties or characteristics of the cigarette. For instance, wrapping paper can be used to adjust the tar delivery per puff, burn rate, puff count, etc. Wrapping paper can also be used to limit the amount of smoke that emanates from the lit end of the cigarette when it is left burning. Further, wrapping paper is even used to reduce the tendency of cigarettes to ignite surfaces which come into contact with the cigarette and to cause the cigarette to self extinguish when left unattended (i.e., ignition proclivity).
One particularly important aspect of the smoking article that can be controlled by the wrapping paper is the smoking article burn rate. For example, a low burn rate can help reduce the ignition proclivity of a smoking article. Moreover, a slower burn rate may also satisfy consumers who desire a smoking article, such as a cigarette, to burn at a relatively slow rate so that an optimum puff count can be achieved.
Recently, due to economic reasons, smoking articles have begun to be produced with lesser amounts of tobacco or with expanded tobacco that is less dense than conventional tobacco, and thus, less costly on a volume basis. However, one significant problem with utilizing less tobacco or expanded tobacco is that the burn rate of the smoking article is significantly increased.
To reduce the burn rate of these or other smoking articles, various techniques have traditionally been utilized. For instance, traditional techniques for lowering the burn rate include decreasing the permeability of the paper wrapper, decreasing the level of burn additive (e.g., citrate), as well as decreasing the filler or chalk level in the paper wrapper. However, in certain instances, it may not be possible or desirable to use these traditional techniques. For example, these techniques may have an adverse affect on other properties of the wrapper.
Thus, a need currently exists for a method of decreasing the burn rate of a smoking article without adversely affecting other characteristics of the resulting smoking article.
The present invention is generally directed to a method for modifying the paper structure to control the burn rate of a smoking article. In one embodiment, for example, the burn rate of the smoking article is reduced by incorporating into the paper a filler having a median particle size larger than about 2.5 microns.
Any filler material may generally be used in the wrapper of the present invention. Such fillers may include, for instance, calcium carbonate, titanium dioxide, magnesium carbonate, magnesium oxides and the like. For example, one suitable calcium carbonate filler can be obtained from Specialty Minerals, Inc. of Adams, Mass., under the tradename ADX 7014, which is a precipitated calcium carbonate material having a median particle size of 3.5 microns.
In addition, the amount of filler added to the paper generally depends upon the desired permeability, opacity, and the particle size of the filler used. Of particular advantage, however, the desired burn rate levels can generally be obtained without substantially modifying conventional filler levels. Thus, for most applications, the total filler level in the paper can be from about 20% by weight to about 45% by weight, and particularly from about 20% by weight to about 30% by weight.
As stated, a filler having a certain median particle size is incorporated into the paper wrapper to reduce the burn rate of the smoking article. For instance, the filler typically has a median particle size of greater than about 2.5 microns. By utilizing fillers with such particle sizes, the burn rate can be significantly reduced.
In particular, paper wrappers of the present invention typically have a Diffusion Conductance Index (DCI) value less than about 15 cmxe2x88x921, and in some embodiments, between about 5 cmxe2x88x921 to about 15 cmxe2x88x921. Moreover, the Static Burn Rate (SBR) of the smoking articles made with paper wrappers of the present invention can be less than about 5.0 millimeters per minute, and in some embodiments, less than about 4.0 millimeters per minute. In addition, it is believed that the paper wrappers of the present invention can provide up to about a 75% reduction in the burn rate of a smoking article as compared to an identical smoking article made with a paper wrapper having a lower filler particle size (e.g., 1.9 microns) at approximately the same permeability, basis weight, burn control additive level, and filler level. For instance, in one embodiment, a paper wrapper of the present invention can provide between about a 5% to about a 20% reduction in the burn rate of a smoking article as compared to an identical smoking article made with a paper wrapper having a lower filler particle size but having the same permeability.
In some embodiments, a paper wrapper of the present invention can also be coated in discrete regions of an ignition-reducing solution to further reduce the burn rate of the paper. In one embodiment, for instance, an aqueous film-forming solution, such as acidified sodium alginate or a cellulosic polymer dissolved in a non-aqueous solvent, can be applied to certain portions of the paper wrapper. The ignition-reducing solution may generally be applied to the wrapper using conventional techniques, such as gravure or flexographic printing. Moreover, the solution can also be applied in a variety of discrete patterns, such as in the shape of bands, crosshatch, ramped, irregular shapes, and the like.
As indicated above, such a reduced burn rate can provide a number of benefits to the resulting smoking article. For instance, a reduced burn rate can reduce the propensity of the smoking article to ignite surfaces or articles with which they contact (i.e., ignition proclivity). In addition, because such a reduced burn rate also results in an increased puff count, smoking articles formed according to the present invention may also appease consumers who desire that the smoking article have an optimum puff count.
Further, it has been discovered that paper wrappers formed in accordance with the present invention can achieve the benefits described above without severely affecting other properties of the smoking article, such as tar delivery, taste, sidestream smoke, and the like. Moreover, it has also been discovered that the desired burn rate reduction can be achieved at relatively low permeabilities, e.g., less than about 60 CORESTA (wherein xe2x80x9cCORESTAxe2x80x9d is defined as the flow of air through a web per unit area of the web at a pressure differential of 1 centibar).
Other features and aspects of the present invention are discussed in greater detail below.